Zombies in Space! The Hungriest Stars You’ll Ever Meet

from The Dark Matter of Science

Illustration by Kathleen Foley

Zombies are usually something we see on movie and television screens, and they pretty much only have a one track mind: Eat humans. They chase people through malls. They chase people through woods. They chase people through pubs. They really need to find a new hobby. Well, in spite of most nerds’ dreams, zombies are fiction.

Or are they?

I’m here to tell you that not only are zombies very real, but they are, in fact, extremely useful. All you have to do to catch a glimpse of one is to look up into the black, and gaze upon one of our universe’s brightest objects:  zombie stars.

Cue shrieks of terror.

But don’t worry. Unlike Sam Raimi’s zombies, these stars have no appetite for human flesh.  But, just like the concept of zombies, when these stars die, they prey on the matter of a living companion star.

A Star’s Afterlife

Going against genre, these hungry stars are beacons of guidance instead of horror.

Zombie stars do have an actual name. They are classified as Type Ia Supernovae, which sounds technical, but doesn’t take anything away from these celestial phenomena. Supernovae are the type of explosion that even Michael Bay will never even achieve. Bad for the box office, but good for movies with plot.

So, what are the ingredients to trigger such an explosion- one so bright that its light can be seen 14 billion light years away?

Well, first you must realize that unlike our Sun, a lot of stars are part of a binary system, which means that two stars are locked together by each others’ gravity and orbit one another.

Eventually, like all things, both stars will die. For our purposes, things get interesting when one of the stars bites the dust first. So, let’s say you have Star A and Star B locked in a binary system. Star A’s life is over, which is to say all of the nuclear reactions in its core has ceased. Basically, Star A has become a white dwarf- a small, very dense star, which, appropriately for this piece, has a core made of Ash.

Anyway, while Star A has, in fact, died, Star B is still going through changes- one of which will be its transformation into a Red Giant. The star turns red and expands. This is actually the step in the star’s life cycle before it becomes a white dwarf.

In Star B’s case, since it’s now bigger and therefore closer to Star A, the dead star’s gravity brings the star to zombie status by sucking in the matter of Star B. It’s this that sets off a nuclear chain-reaction and sparks the zombie star’s stellar explosion.

A white dwarf sucking in the matter of a red giant.

Lighting the Unknown

Type Ia supernovae are some of the brightest explosions around. Again, they can be seen 14 billion light years away. That’s impressive to say the least. But what makes these supernovae so useful is their ability to basically all give off the same amount of light (zombie stars always explode when they reach 1.4 solar masses. That’s 40% more mass than our Sun packed into a smaller star!).

This has been paramount in investigating the great mystery of dark energy.

Our universe is expanding at an accelerated rate. Galaxies are getting farther and farther away from each other. This is odd, since gravity should be pulling everything towards one another. Dark energy is the unknown force that’s negating gravity’s influence and causing expansion.

We may not know much about dark energy- other than it might be an actual property of the fabric of space- but we do know it exists in large part to zombie stars.

As noted by Andy Howell of the University California, Santa Barbara in a recent Yahoo! article:

“We only discovered this about 20 years ago by using Type Ia supernovae, thermonuclear supernovae, as standard or ‘calibrated’ candles,” said Howell. “These stars are tools for measuring dark energy. They’re all about the same brightness, so we can use them to figure out distances in the universe.”

Zombie stars have become our cosmic map.

These scavenging candles in the sky made me realize just how primitive our species still is. On this planet, we use GPS, satellites and computers to get around. My uncle prefers to use the English-accented female voice on his GPS, he has fondly (creepily) called British Jane. A person can travel to the other side of the world from where he or she is currently standing, and the trip can completely be mapped out by any device capable of using Google Maps.

But on a cosmic scale, here we are, relying on dots in the sky to map our way through the universe, like old-time travelers, braving across the oceans for the first time.

As Howell notes in this ScienceDaily piece:

“The next decade holds real promise of making serious progress in the understanding of nearly every aspect of supernovae Ia, from their explosion physics, to their progenitors, to their use as standard candles,” writes Howell in Nature Communications. “And with this knowledge may come the key to unlocking the darkest secrets of dark energy.”

All we are right now are adventurers trying to map out the cosmos with a little help from the living dead.

Off the Rail

Quick and “out there” tib bits

Theorist Walter Cruttenden believes that our Sun is actually part of a binary system- possibly paired up with a brown dwarf. These are weak stars, and thus might be the reason why it’s gone undiscovered so far. So, will our Sun one day eat the matter of this star, if its out there? Well, that’s for the time span of billions of years, and possibly Sam Raimi, to figure out. And if our Sun does, don’t feel bad for it’s victim. Cruttenden believes that this mysterious star is responsible for patterns of mass extinction on Earth.

Also in this section: Often I like to plug scientific concepts into Youtube, and see what visual oddities pop up. The video below is Youtube’s take on Zombie stars.

I’m sorry:

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